The present invention relates generally to chemical mechanical polishing (CMP) of semiconductor substrates.
As industry standards trend toward smaller device features, there is a continuous developing need for new types of metal materials that can be used to replace (W) or copper (Cu) as new electrical conducting interconnection materials in IC chip fabrication and integration, specifically, for 16 nm technology nodes and beyond applications. Cobalt (Co) has been considered and tested as one of the promising new type of metal inter-connection material in IC chip integration. CMP of cobalt interconnect requires polishing of cobalt layer at high removal rates and provide high degree of planarity without introducing corrosion defects. Cobalt interconnect polishing requires removal rates in excess of 1000 Angstroms/minute, which requires slurry compositions which are chemically aggressive to cobalt and yet not cause any corrosion issues.
Unfortunately, existing slurries for polishing of copper or tungsten cannot be used to give satisfactory CMP performance for cobalt interconnect structures. Without being limited to any particular theory, this may be due to cobalt being chemically reactive with the existing polishing slurries, resulting in cobalt dissolution, which in turn leads to a high defect count.
Most of the prior art on cobalt CMP relates to polishing thin cobalt barrier liners underneath the copper interconnects. The requirement of cobalt barrier polishing are quite different from cobalt interconnect polishing. Cobalt barrier polish require cobalt removal rates typically less than 500 Angstroms/min.
US Patent Application 20130186850 or WO2013112490 (Applied Materials) teaches a slurry for chemical mechanical polishing of a cobalt interconnect or a cobalt barrier layer. The slurry includes abrasive particles, an organic complexing compound for Cu or Co ion complexion, a Co corrosion inhibitor that is 0.01-1.0 wt % of the slurry, an oxidizer, and a solvent. The slurry has a pH of 7-12.
US Patent Application 20130140273 teaches slurry for chemical mechanical polishing of Co. The slurry comprises components by weight as follows, inhibitor 0.01-2%, oxidant 0-5%, abrasive 0.1-10%, complexing agent 0.001-10%, and the rest of Water. The pH value of the slurries is adjusted to 3-5 by a pH value adjustor. The inhibitor is chosen from one or more kinds of five-membered heterocycle compound containing S and N atoms or containing S or N atom. The oxidant is one or more chosen from H2O2, (NH4)2S2O8, KlO4, and KClO5. The abrasive is one or more chosen from SiO2, CeO2, and Al2O3. The complexing agent is one or more chosen from amino acid and citric acid. The slurry can effectively prevent Co over corrosion and reduce the polishing rate of Co in the polishing process.
“Fundamental Study of Chemical-Mechanical Polishing Slurry of Cobalt Barrier Metal for Next-Generation Interconnect Process,” Hideak Nishizawa et al., Jpn. J. Appl. Phys., Vol. 49, 05FC03 (2 pages), 2010 show that in slurries with pH 10, a passivation layer is formed on cobalt surface and cobalt-copper galvanic corrosion is minimized.
“The Effect of H2O2 and 2-MT on the Chemical Mechanical Polishing of Cobalt Adhesion Layer in Acid Slurry,” Hai-Sheng Lu et al., Electrochem. and Solid-State Letters, Vol. 15, Issue 4, pp. H97-H100 (2012). The work demonstrates that H2O2 greatly increases the static etch rate (SER) and removal rate (RR) of cobalt. The 2-Mercaptothiazoline (2-MT) is very efficient at inhibiting cobalt corrosion and reducing the SER and RR of cobalt in the acid slurry. In the glycine based slurry at pH=5, by using 2-MT, the corrosion potential difference between Co and Cu can be reduced to a very small value.
“Cobalt Polishing with Reduced Galvanic Corrosion at Copper/Cobalt Interface Using Hydrogen Peroxide as an Oxidizer in Colloidal Silica-Based Slurries,” B. C. Peethala et al., Journal of the Electrochemical Society, Vol. 159, Issue 6, pp. H582-H588 (2012) used colloidal silica-based slurry with 1 wt % H2O2 as the oxidizer and 0.5 wt % arginine as the complexing agent for CMP on cobalt; this slurry showed superior performance (better post-polish surface quality and no pit formation) at pH 10 compared to pH 6 and 8. At pH 10, there is no measurable dissolution of Co and an open circuit potential (Eoc) difference of about 20 mV between Cu and Co, suggestive of reduced galvanic corrosion. The results also suggest that, during polishing, the Co film surface was covered with a passive film, possibly of Co (III) oxides. Addition of 5 mM BTA to this slurry inhibited Cu dissolution rates and yielded a Co/Cu removal rate ratio of about 1.2 while further reducing the Eoc difference between Cu and Co to about 10 mV, both very desirable attributes.
Thus, there is a strong need for the development of innovative Co CMP polishing compositions that can provide high, tunable Co film removal rates, low Co film static etch rates, low barrier film and dielectric film removal rates, high and desirable selectivity of Co vs. barrier films and Co vs. dielectric films, and minimize or eliminate the possible galvanic corrosion at Co/Cu interface.